[The fusion protein critical for the development of the chronic myelo-]monocytic leukemia is the ETV6/PDGFRB fusion and not the reciprocal PDGFRB/ETV6 fusion. In the ETV6/PDGFRB fusion protein the N terminal portion of ETV6, which includes the pointed domain, is fused to the C-terminal two thirds of the PDGFRB protein, conserving the tyrosine kinase domain of PDGFRB. The fusion of the pointed domain of ETV6 in the N-terminal half with the tyrosine kinase domain in the C-terminal half of the fusion partner is characteristic of the class of ETV6/PTK fusions and is found in the fusions of ETV6 with ABL1, ABL2, JAK2, NTRK3, FGFR3 and SYK (Fig. 11) (Table 2) (Papadopoulos et. al., 1995; Cazzaniga et. al., 1999; Knezevich et. al., 1998; Kuno et. al., 2001; Peeters et. al., 1997)

The fusion protein critical for the development of the chronic myelomonocytic leukemia is the ETV6/PDGFRB fusion, and not the reciprocal PDGFRB/ETV6 fusion. In the ETV6/PDGFRB fusion protein the N terminal portion of ETV6, which includes the pointed domain, is fused to the C-terminal two thirds of the PDGFRB protein, conserving the tyrosine kinase domain of PDGFRB. The fusion of the pointed domain of ETV6 in the N-terminal half with the tyrosine kinase domain in the C-terminal half of the fusion partner is characteristic of the class of ETV6/PTK fusions

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and is found in the fusions of ETV6 with ABL1, ABL2, JAK2, NTRK3, FGFR3 and SYK
(Table 4.2 adapted from Bohlander, 2005) (Papadopoulos, 1995; Cazzaniga, 1999; Kuno,
2001).

Table 4.2: Protein tyrosine kinase fusion partner of ETV6

4.3.4. Transcription factors and other fusion partners of ETV6

The ETV6/RUNX1 (ETV6/AML1) fusion is the most common fusion gene in childhood acute
B cell lymphoblastic leukemia (Shurtleff, 1995).